Abstract
This paper presents transmitter and receiver components for a gas spectroscopy system. The components are fabricated in IHP’s 0.13 μm SiGe BiCMOS technology. Two fractional-N phase-locked loops are used to generate dedicated frequency ramps for the transmitter and receiver and frequency shift keying for the transmitter. The signal-to-noise ratio (SNR) for the absorption line of gaseous methanol (CH3OH) at 247.6 GHz is used as measure for the performance of the system. The implemented mixer-first receiver allows a high performance of the system due to its linearity up to an input power of -10 dBm. Using a transmitter-array with an output power of 7 dBm an SNR of 4660 (integration time of 2 ms for each data point) was obtained for the 247.6 GHz absorption line of CH3OH at 5 Pa. We have extended our single frequency-band system for 228 – 252 GHz to a 2-band system to cover the range 222 – 270 GHz by combining corresponding two transmitters and receivers with the frequency bands 222 – 256 GHz and 250 – 270 GHz on single transmitter- and receiver-chips. This 2-band operation allows a parallel spectra acquisition and therefore a high flexibility of data acquisition for the two frequency-bands. The 50 GHz bandwidth allows for highly specific and selective gas sensing.
Highlights
Spectroscopy at mm-wave/terahertz (THz) frequencies is a very powerful tool for high resolution gas spectroscopy because many molecules have rotational transitions in the mmW/THz range.1,2,4–8 With mmW/THz gas spectroscopy it is possible to detect a large number of molecules
That a mixer-first receiver has improved the performance of our spectroscopy system due to its higher linearity compared to our pervious RX as demonstrated by a signal-noise ratio of 4660 for the 247.6 GHz absorption line of CH3OH at 5 Pa
The full spectrum was taken with an acquisition time of 24 s and the integration time of the lock-in amplifier was 2 ms
Summary
Spectroscopy at mm-wave (mmW)/terahertz (THz) frequencies is a very powerful tool for high resolution gas spectroscopy because many molecules have rotational transitions in the mmW/THz range. With mmW/THz gas spectroscopy it is possible to detect a large number of molecules. With mmW/THz gas spectroscopy it is possible to detect a large number of molecules. This technique can provide a profile of volatile organic compounds (VOCs) and toxic industrial chemicals (TICs) in air.. Significant progress has been made in sources based on frequency synthesis techniques starting with a fundamental oscillator in the region around 10 GHz and subsequent frequency multiplication. This has led to the development of mmW/THz spectrometers for molecular absorption spectroscopy.. The source and the detector are driven by a microwave synthesizer The disadvantage of these spectrometers is the high cost of its components. The implementation of integrated mmW/THz components in SiGe BiCMOS or CMOS technology offers a path towards a compact and low-cost system for gas spectroscopy
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